Control system and method for air compressor

ABSTRACT

In a device and a method for controlling an oiled air compressor ( 1 ), which is included in a compressed-air system ( 2 ) for a motor vehicle and which is driven by the engine ( 3 ) of the motor vehicle and supplies compressed air to at least one consumer ( 12 ) in the compressed-air system ( 2 ), provision is made of, on the one hand, a control unit ( 14 ) for controlling the function of the air compressor ( 1 ) by activating the air compressor at a lower predetermined pressure level (P 1 ) for charging the compressed-air system and deactivating the same at a higher predetermined pressure level (P 2 ) for relieving the air compressor, and, on the other, a drainage unit ( 17 ), which in connection with the activation of the air compressor ( 1 ) drains pollutants, which have accumulated in the air compressor during the deactivation, before the air compressor is allowed to start charging the compressed-air system ( 2 ).

FIELD OF THE INVENTION

The present invention relates to a device for controlling an oiled aircompressor, which is included in a compressed-air system for a motorvehicle and which is driven by the engine of the motor vehicle andsupplies compressed air to at least one consumer in the compressed-airsystem, a control unit being provided for controlling the function ofthe air compressor by activating the air compressor at a lowerpredetermined pressure level for charging the compressed-air system anddeactivating the same at a higher predetermined pressure level forrelieving the air compressor. The invention also relates to a method forcontrolling an oiled air compressor, which is included in acompressed-air system for a motor vehicle and which is driven by theengine of the motor vehicle and supplies compressed air to at least oneconsumer in the compressed-air system, the function of said aircompressor being controlled by being activated at a lower predeterminedpressure level for charging the compressed-air system and deactivated ata higher predetermined pressure level for relieving the air compressor.

BACKGROUND OF THE INVENTION

In motor vehicles, in particular heavy goods vehicles, the internalcombustion engine of the vehicle is normally used also to drive suchauxiliary appliances as generators and air compressors. As to aircompressors, they are lubricated with oil and in most cases of pistontype. They are part of compressed-air systems for supplying variousconsumers, such as brakes and air suspension, in the vehicle withcompressed air. The supply of lubricating oil to the air compressor isoften connected with the internal combustion engine, such that the samelubricating oil is used for both.

For a long time, problems have arisen owing to lubricating oil from theair compressor being entrained into the system by the generatedcompressed air. The entrained lubricating oil is present in liquid aswell as evaporated form and causes problems in the brakes, the airsuspension etc, in the form of general messiness andswelling/degradation of primarily rubber packings.

Since the air compressor is driven by the internal combustion engine allthe time and thus rotates constantly, whereas the generation ofcompressed air or charging is needed about 20-50% of the time, a systemfor controlling the charging is wanted. This may be achieved by means ofa control unit, for instance a regulator, which activates the aircompressor at a lower minimum pressure in the order of say 7.5 bar anddeactivates the same at a higher maximum pressure in the order of say12.5 bar.

The deactivation may be achieved by relieving the air compressor.Preferably, this is carried out by preventing the air compressor fromcharging air by blocking its outlet. The blocking may be provided by ashut-off device in the form of a stop valve or the like, which iscontrollable by the control unit. This means that the air compressor,which is still rotating, accumulates the lubricating oil which is neededfor the lubrication of the compressor pistons and blows past the pistonrings during the entire deactivation phase, that is until the renewedactivation at the minimum pressure.

When the air compressor is activated and starts charging thecompressed-air system by generating compressed air, the storedlubricating oil in liquid and evaporated form is entrained by thecompressed air into the system. This is also the case of condensate andother pollutants which may have formed during the deactivation phase inthe compressor cylinders by the relieving of pressure/cooling. If adryer is also arranged in conventional manner downstream of the aircompressor in the compressed-air system, a portion of the pollutants iscaptured by the air dryer. However, above all the evaporated portion ofthe lubricating oil passes the air dryer and is thenprecipitated/condensed in the brakes and the air suspension etc, causingthe above-mentioned damage.

It is true that pollution of the above-described type also occurs whenthe air compressor is activated and generates compressed air. The totalamount of pollutants is, however, completely decisive of how fast theproblem arises.

In order to solve this problem to some extent, a so-called lineonloader-system may be used. This means that the air compressorgenerates compressed air constantly and that excess air, whendeactivating, is exhausted to atmosphere via a valve or the like, whichcan be provided in the air dryer. A great problem of this method is thehigh fuel consumption of the internal combustion engine. For instance,when driving 200,000 km, use is made of about 1000 l more fuel a yearthan in the case where the air compressor is deactivated.

OBJECT OF THE INVENTION

An object of the present invention is to make it possible to apply aninexpensive, space-saving and efficient solution to the problem ofpollution in the compressed air after the deactivation phase in the aircompressor.

SUMMARY OF THE INVENTION

This object is achieved by a device of the type defined by way ofintroduction by means of a drainage unit, which in connection with theactivation of the air compressor drains pollutants, which haveaccumulated in the air compressor during the deactivation, before theair compressor is allowed to start charging the compressed-air system.In the method according to the invention, the object is achieved bydraining, in connection with the activation of the air compressor,pollutants which have accumulated in the air compressor during thedeactivation, before the air compressor starts charging thecompressed-air system.

BRIEF DESCRIPTION OF THE DRAWING

Below, the invention will be described in detail with reference to theaccompanying drawing. It illustrates a simple connection diagram of apreferred embodiment of the device according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The device according to the invention, which is shown in the drawing, isin particular, but not exclusively, intended to be used in heavy motorvehicles, such as lorries and buses.

The device comprises an oiled air compressor 1, which is included in acompressed-air system generally designated 2 and intended for a motorvehicle (not shown). The air compressor 1 is of piston type and fixedlyconnected to an internal combustion engine 3, e.g. a diesel engine, tobe driven constantly by the same. The connection may be provided bymeans of a suitable connection 4 in the form of, for instance, a driveshaft.

Moreover, the air compressor 1 has an inlet 5 for the supply ofatmospheric air and an outlet 6 for the compressed air generatedtherein. More specifically, the compressed air is fed from the outlet 6via a conduit 7 an air dryer 8 for drying the entering compressed air.Instead of the air dryer 8, some other suitable device may be providedfor conditioning the compressed air. In some cases, the air dryer 8 maybe omitted.

The dried compressed air is then fed on to an air tank or accumulator 9of conventional design via a conduit 10. The accumulator 9 is in itsturn connected in a suitable manner to one or more consumers. Thedrawing schematically shows how it is connected via a conduit 11 to aconsumer 12, for instance the vehicle brakes, air suspension etc.

In the illustrated embodiment, the accumulator 9 is connected to acontrol unit 14 via a control conduit 13. The control conduit 13 can bea compressed air conduit or an electric signal line. The control unit 14may be a pressure regulator and serves to control the function of theair compressor 1 depending on the system pressure in the compressed-airsystem 2. For this reason, the control unit 14 is connected to the aircompressor 1 in a manner described below, via an additional controlconduit 15, substantially corresponding to the control conduit 13.

The control unit 14 controls the function of the air compressor byactivating the air compressor at a lower, predetermined pressure levelP₁ for charging the compressed-air system 2 and deactivating the same ata higher, predetermined pressure level P₂ for relieving the pressure inthe air compressor 1. As an example, it can be mentioned that the lowerpressure level P₁ can be a minimum pressure in the order of 7.5 bar andthe higher pressure level P₂ can be a maximum pressure in the order of12.5 bar. These pressure levels are only examples and may be varied bothupwards and downwards.

The deactivation of the air compressor is controlled by the control unit14 and is provided, as mentioned above, by the relieving of the pressurein the air compressor. More specifically, this may be provided byblocking the air compressor 1, thus preventing it from charging thecompressed-air system 2 with compressed air. The blocking may beachieved in many different ways. In the shown embodiment, the blockingis carried out by means of a shut-off device 16 which is placed at theoutlet 6 of the air compressor 1. This device 16 may be in the form of astop valve or the like. The above-mentioned control conduit 15 from thecontrol unit 14 is then connected to the shut-off device 16 to open andclose the same for activation and deactivation of the air compressor 1.

A drainage unit, generally designated 17, is also included in thecompressed-air system. In connection with the activation of the aircompressor 1 at the lower pressure level P₁, the drainage unit serves todrain pollutants, i.e. lubricating oil in liquid and evaporated form,condensate etc, which have accumulated in the air compressor 1 duringthe preceding deactivation phase, before the air compressor is allowedto start the charging proper of the compressed-air system 2 withcompressed air.

The drainage unit 17 may be placed in the air compressor 1 itself on itsoutlet side or downstream of the air compressor 1 in the conduit 7. Inthe shown embodiment, the preferred position is shown, that is inconnection with or integrated in the air dryer 8. The drainage unit 17may have the form of a pressure-controlled discharge valve having adischarge 18, which for efficient drainage is suitably located at thelowest point in the compressed-air system 2.

Irrespective of the position of the drainage unit 17, it is hereconnected to the control unit 14 via yet another control conduit 19.When the control unit 14 sends a signal via the control conduit 15 tothe shut-off device 16 of the air compressor 1 to open the same and thusactivate the air compressor, it also sends a signal via the controlconduit 19 to the drainage unit 17 to open the discharge 18 for drainingthe pollutants from the air compressor 1. When the air compressor 1,after the opening of the shut-off device 16, has rotated a suitablenumber of turns and discharged all its pollutants via the conduit 7 andthe discharge 18 of the drainage unit 17, the drainage unit 17 isclosed, so that the compressed air which is now generated by the aircompressor can be fed on in the compressed-air system 2 to the consumer12.

If the drainage unit 17 is placed inside the air compressor 1, it may beso arranged that it opens for drainage of the pollutants, before the aircompressor is activated by the opening of the shut-off device 16.

The invention is not to be considered to be limited to the embodimentwhich is described above and shown in the drawing, and may be modifiedin many different ways within the scope of the appended claims.

What is claimed is:
 1. A compressed air device, comprising: a compressedair system including an oiled air compressor, the compressed-air systemsupplying compressed air to at least one consumer in the compressed-airsystem; a control unit for controlling functioning of the aircompressor, the control unit being adapted to activate the aircompressor at a first predetermined pressure level for charging thecompressed-air system and being adapted to deactivate the air compressorat a second predetermined pressure level; and a drainage unit thatdirectly drains pollutants that accumulate in the air compressor duringdeactivation of the air compressor, the drainage unit being arranged inthe compressed-air system so that the pollutants are drained before theair compressor starts charging the compressed-air system.
 2. A device asclaimed in claim 1, wherein the drainage unit is disposed downstream ofthe air compressor and has a discharge at a lowest point in thecompressed-air system.
 3. A device as claimed in claim 2, wherein adryer for the compressed air is provided between the air compressor andthe consumer, and the drainage unit is connected to the dryer.
 4. Adevice as claimed in claim 1, wherein a dryer for the compressed air isprovided between the air compressor and the consumer, and the drainageunit is connected to the dryer.
 5. A device as claimed in claim 4,wherein the drainage unit is integrated in the dryer.
 6. A device asclaimed in claim 1, wherein the drainage unit includes a discharge thatis adapted to open and close, the control unit being adapted to send asignal to the discharge to open the discharge when the control unitactivates the air compressor.
 7. A device as claimed in claim 1, whereinthe drainage unit is disposed downstream of the air compressor.
 8. Adevice as claimed in claim 1, wherein the drainage unit has a dischargeat a lowest point in the compressed air system.
 9. A method foroperating a compressed air system including an oiled air compressorcomprising: activating the air compressor at a first predeterminedpressure level for charging the compressed-air system; deactivating theair compressor at a second predetermined pressure level; and before theair compressor starts charging the compressed air system, directlydraining pollutants that accumulate in the air compressor duringdeactivation in a drainage unit.
 10. A method as claimed in claim 9,wherein the drainage unit includes a discharge that is adapted to openand close, the discharge being opened when the air compressor isactivated but before the air compressor charges the compressed-airsystem.
 11. A method as claimed in claim 9, wherein the drainage unit isdisposed downstream of the air compressor.
 12. A method as claimed inclaim 9, comprising discharging drained pollutants at a lowest point inthe compressed air system.